Freestyle : problem with visibility
Your issue comes from your object design : the cylinder and the circle should be in a single object + the circle should have a thickness + The circle should be an extrusion of a ring of the cylinder.

The idea is to create the cylinder, to add a loop on this cylinder and to extrude this loop to create the cicle.

Here is a full how to :


Create a new project
Delete the cube
Add a cylinder : press Shift + A then select Mesh and Cylinder
Enter in edit mode (TAB)
Press S then Z to enable Z scrolling
Move the mouse to increase the hight of the cylinder. 
Press ENTER to validate.
Move the mouse cursor in the center of the cylinder
Press CTRL + R to add a loop cut : a pink horizontal circle should appear at the middle of the cylinder like this : 





Scroll up the middle mouse button to have 2 pink circles like this : 





Press the left mouse button
Move the mouse up to place the new ring
Press the left mouse button to validate
Enable the Face select mode (CTRL + TAB and select Faces)
move the mouse cursor on a vertical edge of the middle ring you have just created
Press ALT + RMB : this ring should be selected (in orange) like this : 





Press E to extrude this ring and press LMB to validate immediatly (without moving the mouse)
Press S to scall the ring and Shift + Z to lock Z scalling
Move your mouse to increase the diameter of the ring like this : 





Press LMB to validate


To enable Freestyle :


exit Edit Mode (TAB)
in the Render panel, enable the Freestyle option
launch render (F12)


Here is the result (after adding materials and reducing the circle thickness :